Pr\ue9vention de la d\ue9t\ue9rioration du b\ue9ton due \ue0 la r\ue9action alcalis-granulats

La r\ue9action alcalis-granulats est une cause courante de fissuration du b\ue9ton, qui entra\ueene des dommages importants aux constructions en b\ue9ton partout dans le monde. Dans ce num\ue9ro, on explique les m\ue9canismes de la r\ue9action alcalis-granulats, ses effets sur le b\ue9ton et les m\ue9thodes pour pr\ue9venir une d\ue9t\ue9rioration de cette nature dans les nouvelles constructions.Alkali-aggregate reaction is a common cause of concrete cracking that results in significant damage to concrete structures worldwide. This Update explains the mechanisms of alkali-aggregate reaction, its effects on concrete and methods for preventing deterioration from this cause in new construction.Also available in English: Preventing Concrete Deterioration Due to Alkali-Aggregate ReactionPeer reviewed: NoNRC publication: Ye

Development of a universal accelerated test for alkali-silica and alkali-carbonate reactivity of concrete aggregates

A universal accelerated test for both alkali-silica and alkali-carbonate reactivity was proposed based on extensive comparative studies on existed Accelerated Mortar Bar Test (AMBT), (e.g., ASTM C1260, CSA A23. 2-25A, RILEM TC191-ARP-AAR02) and Chinese accelerated procedures. A single size fraction of 2.5-5.0 mm aggregate particles is used in the test instead of five-graded requirements in the AMBT, and 0.15-0.80 mm fine particles for ASR, 5-10 mm particles for ACR in existed Chinese accelerated tests. Three short-fat bars, 40 × 40 × 160 mm, made at fixed cement-aggregate ratio of 1:1, and water-cement ratio of 0.33 are used and the length change of the bars is monitored till 28 days in 1 M NaOH solution at 80°C after being soaked in 80°C water for 24 h. Over 40 kinds of aggregates from various origins, which include both ASR and ACR aggregates and show a broad range of reactivity levels in the concrete prism test (CPT), were used to evaluate the reliability of the new test in this study. Experimental results indicate that, for ASR aggregates, the new test gives a better indication than the AMBT does of both the reactive/nonreactive characteristic and reactive levels of almost all tested aggregates based on an acceptance criteria of 0.093% at 14 days, although some very highly reactive aggregates show low expansions relative to the CPT. The "abnormal" low expansion of some highly reactive aggregate in the test is mainly due to the rapid formation and loss of fair amount of low viscosity ASR product into the soaking alkali solution. The results on some typical ACR aggregates usually undetected by the AMBT show that the new test gives the same outcome as using 5-10 mm particles in the Chinese Accelerated Concrete Microbar Test for ACR aggregates and is in agreement with the CPT, which suggests that it has good potentials to be used for ACR aggregate when an expansion criteria of 0.1% after 28 days is used. © 2007 RILEM has copyright